Fixing device for an oscillatory crystal

ABSTRACT

A wire suspension device for oscillatory piezoelectric crystals made of a bar vibrating in a flexion mode, said wires being fixed on two parallel faces at points of minimum vibration of the crystal , determined by the intersection with these faces of a particular inclined straight line passing through a point of the median axis of longitudinal symmetry located at a distance from one end of approximately 0.2 times the total length.

United States Patent [1 1 Gibert et al.

[111 3,794,867 Feb. 26, 1974 FIXING DEVICE FOR AN OSCILLATORY CRYSTAL lnventors: Guy Gibert; Pierre Vidal, both of Sartrouville, France Assignee: Compagnie DElectronique Et De Filed:

Piezo-Electricite-C.E.P.E., Paris, France Feb. 9, 1972 Appl. No.: 224,879

Foreign Application Priority Data Feb. 19,1971

US. Cl 310/9.l, 3 10/94, 3.10/82 Int. Cl...., H01v 7/00 Field of Search 310/82, 9.1, 9.4

References Cited UNITED STATES PATENTS Omlin 310/9.1

France 71.0575l 3,221,189 11/1965 Brandt et al. 310/9.1

2,282,369 5/1942 Mason BIO/9.5

2,410,825 11/1946 Lane...- 310/95 2,395,434 2/1946 Tenenbaum 310/96 X Primary Examiner-William M. Shoop, Jr.

Assistant Examiner Mark O. Budd Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT A wire suspension device for oscillatory piezoelectric crystals made of a bar vibrating in a flexion mode, said wires being fixed on two parallel faces at points of minimum vibration of the crystal determined by the intersection with these faces of a particular inclined straight line passing through a point of the median axis of longitudinal symmetry located at a distance from one end of approximately 0.2 times the total length.

4 Claims, 4 Drawing Figures PAIENIE F552 6 I974 FIXING DEVICE FOR AN OSCILLATORY CRYSTAL The present invention relates to oscillatory crystals for time-base purposes, these conventionally being electrically sustained by piezoelectric effect through suitably disposed electrodes, and the material of which they are made being usually constituted by a quartz crystal cut in particular directions which are associated with its cryatal lattice.

In the case of the low frequencies, ranging for example from some few kilohertz per second up to some few tens of megahertz per second, the crystal elements used.

take the form of elongated bars whose section is nearsquare, equipped with electrodes whose shape and disposition are such that the resultant vibrations involve a bending or flexion motion of the whole bar.

However, the need to attach the vibrating crystal in mountings, normally by soldering operations, creates a substantial difficulty, namely that of the transmission of mechanical energy from the crystal to its mountings or supporting arrangements, and this in turn means that modifications to the operating characteristics of the crystal on its own, are introduced moreover, said modifications develop over a period of time, as a consequence of the aging of the soldered joints referred to These phenomena can be reduced by selecting on the crystals, as points of attachment for the suspension elements, particular points where the amplitude of the vibration is at a minimum. In the prior art, these points are selected on the longitudinal axes of the fixing faces, at special distances from the ends which, considering the flexion mode of vibration, are made equal to 0.224 times the length of the bar.

However, this usual choice is based upon calculations for the case of homogeneous oscillatory bars, taking no account of the orientated and anisotropic character of the piezoelectric crystals which are used in fact, nor in particular of the asymmetric shear effects resulting from the bending fiexion. The result is that excessive alternating stresses are developed in the zones comprising the soldered fixings of the bars, with consequent change in their characteristics over a period of time and ultimately a notable variation in the generated frequency.

The present invention relates to a fixing device for crystal mounting which does not exhibit this drawback and more precisely to a fixing device for a crystalline parallelepiped bar capable of mechanical oscillations in a flexion mode and in a plane parallel to that of the faces by which said parallelepiped is fixed, said fixing faces being parallel with one another, comprising a fixed support, and suspension wires, respectively attached at one of their ends to said support and at the other end to the crystal, at fixing points on said faces, said points being arranged in pairs respectively on each of said faces, and each pair of points being located on a straight line intersecting the median plane of symmetry of the bar which is parallel to said faces, said intersection point being located on the axis of symmetry of said median plane of the bar, and said straight line making an angle ranging between and with the direction perpendicularto said faces.

The invention will be better understood from a consideration of the ensuing description and by reference to the attached drawing in which FIG. 1 illustrates a crystal fixing device, of prior art design FIG. 2 illustrates a fixing device in accordance with the invention;

FIG. 3 illustrates a diagram FIG. 4 illustrates a variant embodiment of the device in accordance with the invention.

FIG. 1 illustrates an oscillatory bar equipped with fixing points chosen in accordance with the prior art. The bar is cut in the form of a rectangular parallelepiped from a quartz crystal, the corners of said parallelepiped being orientated in particular directions associated with the crystal lattice, in order to achieve characteristics of oscillation which accord with the applications envisaged.

For example, the crystallographic axes X, Y and Z, being respectively the electrical axis, the mechanical axis and the optical axis, it is known to cut a crystal bar so that its corners or edges have directions parallel to the axes X, Y, Z',-the axes Y, Y and Z, Z making an angle 0 with one another which is usually around 5 counted in the trigonometric sense, this kind of cut giving the bar characteristics of minimum temperatureinduced frequency drift. In a bar of this kind, the fixing points A A A and A, are, as has already been indicated, arranged upon the axis of symmetry of each of the two fixing faces at a distance from the ends equivalent to 0.224 times the bar length, and constitute the points of attachment for suspension wires such as those 4 and 5 which are attached on the other hand to a fixed support 10 which has not been shown in full.

FIG. 2 illustrates a suspension device in accordance with the invention. It comprises suspension wires such as 4 and 5, attached on the one hand to a fixed support (not shown) and on the other to the crystal bar by means of fixings, in the form of solder for example, produced at the points A,, A A and A located at particular positions on the fixing faces. These positions can be defined by the intersections between a particular straight line D and the planes of the fixing faces: The straight line D is contained in the plane of symmetry 6 of the bar, which is parallel to the axis Z and makes an angle alpha in relation to the perpendicular to the fixing faces 11 and 12, as well as in relation to the plane of symmetry 7 of the bar, which is parallel to the plane X Y. The value of a depends upon the ratio of the thickness 15 to the width 16 of the bar, said angle a being measured in the reverse sense, that is to say in the clockwise sense.

Moreover, the straight line D intersects said plane of symmetry 7 of the bar which is parallel to the plane X Y, at a point B which, in relation to the end thereof, is at a distance of less than 0.224 times the bar length, and may be as little as 0.2 times the bar length.

The determination of these new positions for the fixing points has been based upon theoretical calculations checked by pratical trials, and taking into account the shear forces, in association with the anisotropy of the crystalline material used.

FIG. 3 illustrates a diagram showing the order of magnitude of the above-defined angle alpha as a function of the dimensions of the bar, and in fact of the ratio R between the thickness 15 and width 16 thereof.

F l6. 4 illustrates a variant embodiment of the fixing device in accordance with the invention.

It comprises the same suspension elements as the device of FIG. 2 but the fixing points have been placed at locations A' and A' located on special straight lines G and G on the fixing faces, which lines pass through the points A, A A A already defined, and are inclined in relation to the axis of symmetry of each fixing face, at an angle beta ranging between 30 and 60 the fixing points are on the other hand, as FIG. 2 already indicates, respectively located at the points of intersection between a straight line D passing through the point B and said straight lines G and G this putting said points at either side of that plane of symmetry of the bar which is parallel to the plan Y Z, and making it possible to arbitrarily choose as fixing points any point located on these straight lines.

By way of example, the results obtained with crystal bars comprising the fixing device in accordance with the invention include, when compared with identical bars fitted with the device of the prior art type, a Zero temperature coefficient in a bar raised from 28 to 49, and a time-based frequency shift of the bar which is around times less.

Of course, the invention is not limited tothe embodiment described and shown which was given solely by way of example.

What is claimed is:

1. A fixing device for an oscillatory crystal in parallelpiped bar form, capable of mechanical oscillations in a flexion mode and in a plane parallel to that of the faces by which said parallelpiped is fixed, said fixing faces being parallel with one'another, comprising a fixed support, and suspension wires respectively attached at one of their ends to said support and at the other end of the crystal, at fixing points on said faces, said points being arranged in pairs respectively on each of said faces, and each pair of points being located on a straight line intersecting the median plane of symmetry of the bar which is parallel to said faces, said intersection point being located on the axis of symmetry of said median plane, said straight line making an acute angle upto 20 with a line passing at said intersection point and perpendicular to said faces.

2. A fixing device as claimed in claim 1, wherein the shorter distance of said intersection point to one of the two ends of the bar is between 0.200 and a value less than 0.224 times the largest dimension of said bar,

3. A fixing device as claimed in claim 1, wherein the plane defined by said straight line and said perpendicular direction,,makes an anglewith the median plane of symmetry of the bar perpendicular torsaid faces, of between 30 and 60.

4. An oscillatory crystal as claimed in claim 1,

equipped with said fixing device. 

1. A fixing device for an oscillatory crystal in parallelpiped bar form, capable of mechanical oscillations in a flexion mode and in a plane parallel to that of the faces by which said parallelpiped is fixed, said fixing faces being parallel with one another, comprising a fixed support, and suspension wires respectively attached at one of their ends to said support and at the other end of the crystal, at fixing points on said faces, said points being arranged in pairs respectively on each of said faces, and each pair of points being located on a straight line intersecting the median plane of symmetry of the bar which is parallel to said faces, said intersection point being located on the axis of symmetry of said median plane, said straight line making an acute angle up to 20* with a line passing at said intersection point and perpendicular to said faces.
 2. A fixing device as claimed in claim 1, wherein the shorter distance of said intersection point to one of the two ends of the bar is between 0.200 and a value less than 0.224 times the largest dimension of said bar.
 3. A fixing device as claimed in claim 1, wherein the plane defined by said straight line and said perpendicular direction, makes an angle with the median plane of symmetry of the bar perpendicular to said faces, of between 30* and 60*.
 4. An oscillatory crystal as claimed in claim 1, equipped with said fixing device. 